Subject: [Sip] Query about '491 response' in case of RE-INVITE.

From: "Manjeet Soodan" <[email-masked]>
Date: Fri, 18 Nov 2005 00:28:24 +0530

1) There are two SIP UA's A and B.
2) A sends INVITE with SDP to B.
3) B responds with 100 and then 180 Ringing(wthout SDP)  and adds TO tag to
180.
3) After 180 is received, A sends a  RE-INVITE before 200 OK is received
(i.e RE-INVITE with all the headers having same value as initial INVITE and
higher CSEQ value).
4) In this case B responds with a  '491 Request Pending' for RE-INVITE.

Is it the right behaviour, if not then what should be the right behaviour of
B?

-Manjeet

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From: Ramesh <[email-masked]>
Date: Mon, 21 Nov 2005 08:55:23 -0700

I think it is wrong to send the 491 in this case. 491 response can only be
sent by A to B, in your example, if B sends an INVITE to A. A can send
multiple Invites as these are nothing but updates to the original. If you
look at the ISUP-SIP overlap signaling ( RFC 3578) you will see this
scenario described when SAM messages are sent.

Cheers
Ramesh

--
cheers
ramesh